The present invention relates to an arrangement for and a method of uniform illumination of a projection surface.
In particular, it relates to such an arrangement which has a light source and optical elements arranged between the light source and a projection surface wherein the distance between the light source and the optical elements is adjusted.
Arrangements of the above mentioned general type are known in the art. One of such arrangements is disclosed for example in the German document DE-OS 2,412,875. In this arrangement the user can change the position of the lamp relative to an optical system so that a maximum uniform illumination of the projection surface is obtained. This method however has the disadvantage in that the user must manually adjust the position of the light source and adjustment in addition depends on the subjective judgment of the user. With the use of alternating objectives with different focal distance or the zoom objectives with changing focal distances, a special adjustment of the illumination by the user is required for each focal distance. The adjustment requires a certain time or when the adjustment is maintained, a not satisfactory illumination of the projection surface is produced.